The present invention relates to a method of forming a groove in a semiconductor laser diode and a semiconductor laser diode having the groove. More in particular, the present invention relates to a method of forming a groove, which can form a groove of a definite shape easily and at a good reproducibility, as well as a novel semiconductor laser diode having such a groove formed by etching to eliminate a portion of a current blocking layer grown over an active layer, which is improved such that the shape of the groove formed in the current blocking layer can be defined easily and at a good reproducibility. The method of forming the groove according to the present invention also includes a method of forming a ridge in the meaning that the ridge is formed between the grooves.
A number of semiconductor laser diodes having a groove in the semiconductor laser diode have been proposed so far. Specifically, there can be mentioned, for example, a semiconductor laser diode having a groove formed by etching to eliminate a portion of a current blocking layer grown over an active layer, and a semiconductor laser diode having a ridge formed by etching to eliminate a portion of an upper clad layer grown over an active layer, the ridge being formed configurationally between grooves. Accordingly, the method of forming the groove is important in the fabrication of the semiconductor laser diodes.
In a semiconductor laser diode having a groove formed by etching to eliminate a portion of a current blocking layer grown over an active layer, since current blocking is conducted by the remainder, it is important to prevent large side etching caused by the wet etching process upon fabrication of the laser diode and to form a groove of a definite shape, particularly, a groove having a constant bottom width at a good reproducibility. That is, if the bottom width of the groove changes greatly by the side etching caused by the wet etching process upon fabrication of the laser diode, a threshold current fluctuates, for example, near field pattern of a laser diode has no reproducibility, and discrete chips obtained from the same wafer have distribution of characteristics.
It has been desired to provide a method of forming a groove capable of forming a groove of a definite shape easily and at a good reproducibility, and further, a method of forming a groove while preventing large side etching.
It has, further, been desired to provide a novel semiconductor laser diode improved such that the shape of a groove formed on a current blocking layer can be fined easily and at a good reproducibility.
As a result of the present inventions' earnest studies for satisfying the foregoing demands, it has been found that: by using a structure of sandwiching a layer comprising MP (wherein M represents one or more of elements belonging to the group IIIb of the periodic table) with layers comprising MAs (wherein M represents one or more of elements belonging to the group IIIb of the periodic table), when a selective etching of the MP layer using the upper MAs layer as an etching mask layer and the lower MAs layer as an etching stop layer is performed, the side etching is restricted, and then, on the basis of the above-mentioned findings, it has been further found that:
by epitaxial growth of a core layer comprising MP (wherein M represents one or more of elements belonging to the group IIIb of the periodic table) and an upper layer comprising MAs (wherein M represents one or more of elements belonging to the group IIIb of the periodic table) successively on (100) surface of MAs crystals in the lower layer comprising MAs, after depositing an etching mask on the upper layer, forming an etching window to the etching mask, and performing a selective etching of the upper layer and other faces except for the face in which (111) face of the MP crystal in the core layer is exposed, PA1 a groove of a definite shape can be formed easily and at a good reproducibility, the bottom width of the groove can be controlled easily while restricted side etching, and since a semiconductor laser diode having such a groove can be obtained in the same wafer uniformly, laser diodes obtained from the same wafer showing little dispersion of the horizontal near field pattern and threshold value can be produced at a good reproducibility. PA1 each of the etching stop layer and the cap layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; and (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer. PA1 the etching stop layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; and (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer. PA1 the etching stop layer at the bottom of the groove formed in the current blocking layer being eliminated by wet etching; each of the etching stop layer and the cap layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; and (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer. PA1 the etching stop layer at the bottom of the groove formed in the current blocking layer being eliminated by wet etching; the etching stop layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; and (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer. PA1 each of the etching stop layer and the cap layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer; and PA1 the groove being formed by a photolithography and wet etching procedure of, after fabricating an etching mask on the cap layer, forming an etching window to the etching mask, a first etching procedure of selective wet etching the cap layer, and a second etching procedure of selective wet etching other faces except for the face in which (111) face of MP crystals in the current blocking layer is exposed. PA1 the etching stop layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer; and PA1 the groove being formed by a photolithography and wet etching procedure of, after fabricating an etching mask on the cap layer, forming an etching window to the etching mask, a first etching procedure of selective wet etching the cap layer, a second etching procedure of selective wet etching other faces except for the face in which (111) face of MP crystals in the current blocking layer is exposed, and a third etching procedure of selective wet etching the cap layer. PA1 the etching stop layer at the bottom of the groove formed in the current blocking layer being eliminated by wet etching; each of the etching stop layer and the cap layer comprising MAs, wherein M represents one or more of elements belonging to the group IIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer; and PA1 the groove being formed by a photolithography and wet etching procedure of, after fabricating an etching mask on the cap layer, forming an etching window to the etching mask, a first etching procedure of selective wet etching the cap layer, a second etching procedure of selective wet etching other faces except for the face in which (111) face of MP crystals in the current blocking layer is exposed, and a third etching procedure of selective wet etching the portion where corresponds to the groove bottom of the etching stop layer. PA1 the etching stop layer at the bottom of the groove formed in the current blocking layer being eliminated by etching; the etching stop layer comprising MAs, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; the current blocking layer comprising MP, wherein M represents one or more of elements belonging to the group IIIb of the periodic table; (111) face of MP crystals in the current blocking layer being exposed on wall surface of the groove formed in the current blocking layer; and PA1 the groove being formed by a photolithography and wet etching procedure of, after fabricating an etching mask on the cap layer, forming an etching window to the etching mask, a first etching procedure of selective wet etching the cap layer, a second etching procedure of selective wet etching other faces except for the face in which (111) face of MP crystals in the current blocking layer is exposed, and a third etching procedure of selective wet etching both of the cap layer and the etching stop layer.
The present invention has been accomplished based on the above-mentioned findings.